1. Field of the Invention
The invention relates to a telescopic system.
2. Description of the Related Art
Telescopic systems include mechanisms constituted by several modules which, at random, can be unfolded/extended or folded in one another, or optionally alongside one another in order to regulate their total length.
Telescopic systems are encountered in numerous technical fields such as cranes, ladders or appendages of robots in order to reach an object having a variable distance or for other functions, specific to each apparatus in which they are incorporated. In the case of robots walking on a series of legs distributed into two sets and which alternatively touch the ground in order to support the robot and are then raised and advanced, telescopic mechanisms equipping the legs in order to shorten and lengthen them make it possible to achieve this procedure in a simple manner, because it is merely necessary to slide the legs along the robot in order to advance the same once they have been raised from the ground. The legs can remain straight and it is pointless to subdivide them into sections articulated to one another and to the robot in order to attempt to reproduce human walking procedure, which requires a more complex structure and causes balance problems.
A first distinction will be made by only attaching interest to mechanisms for which the extension path is greater than the length of the mechanism in the folded state, which imposes the use of at least two modules having an extensible elongation element (such as a sliding tube) and a mechanism joining said elongation element to a preceding elongation element or to a fixed element serving as a base for the mechanism in order to vary the distance separating them and thus controlling the extension of the elongation element. The system is then complicated by the need of adding mechanical links for joining the mechanisms in order to control simultaneously or successively the extension of all the elongation elements.
A current telescopic system used for certain hydraulic cranes consists of several concentric tubes interconnected by jacks arranged in series and communicating with one another by fluid pipes, so that a single pressure source can successively extend them. The control is then ensured by a single action. A multiple action, single jack, i.e. formed by several fitted together, sliding cylinders can also be used with the same advantage. However, jacks are relatively heavy and cumbersome means, which also require flexible supply cables and sensors complicating their installation. Thus, this solution cannot be used in applications such as robotics, where the aim is to reduce to the greatest possible extent the overall weight of the system and the overall dimensions of the control and monitoring means.
A completely different system consists of providing the extension elements with pulleys and cables interconnecting them forming zig-zags. It is sufficient to pull on one cable end in order to simultaneously raise the elements. This system, used for certain ladders and elevators, is characterized by a lack of rigidity, which can be vital for firefighters or furniture removers who have to dock the ladder with a building, but which is unacceptable in other applications, having the disadvantages of limited loading capacity and a problematical behavior of the cables and pulleys over time.
A more complicated system although relatively simple to construct, which has a relatively low weight and a good rigidity, is described with the aid of FIG. 1. It has been used in a robot and consists of three extension modules 1a, 1band 1c, whereof each comprises a screw 2, a nut 3 engaged with the screw 2, an entry pulley 4 fixed to the rear end of the screw 2, an exit pulley 5 fixed around the nut 3 and coaxial thereto, a screw bearing surface 6 towards the rear of the screw 2 but in front of the pulley 4, a nut bearing surface 7, a rear stop 8 located on the screw 2 just in front of the screw bearing surface 6 and a front stop 9 located well in front of the screw 2. The essential elements of these stops 8 and 9 are springs coaxial to the screw 2.
The entry pulley 4 of the intermediate module 1bis connected by a belt 10 to the exit pulley 5 of the first module 1a and the exit pulley 5 of the module 1b is connected by another belt 11 to the front pulley 4 of the third module 1c. Finally, a third belt 12 connects the pulley 4 of the first module la to a driving pulley 13 of a motor 14 fixed to a frame 15.
Each of the modules 1 has a tube 16 provided with a bearing 17 for the nut bearing surface 7 of said module and a bearing 18 for the screw bearing surface 6 of the following module, obviously with the exception of the tube 16 of the third module 1c, which is the last in the system and consequently has no bearing 18. The tubes 16 are concentric, slide in one another and in an external tube 19 rising from the frame 15 to which it is joined And carrying a bearing 20 for the screw bearing surface 6 of the first module 1a. Elementary mechanical devices, which are not shown, such as slides, channels or fittings with polygonal sections, joint the tubes 16 and 19 to one another and prevent them from turning freely, whilst still enabling them to slide.
The starting up of the motor 14 rotates the screw 2 of the first module 1a and nut 3 remains stationary in rotation and moves in translation, driving the tube 16 of the first module 1a and the other modules 1b and 1c until they reach one of the stops 8 and 9 as a function of the rotation direction of the motor 14. The nut 3 is then locked and is rendered integral with the screw 2 and transmits its rotation to the screw 2 of the last module 1b by the belt 10, which displaces the nut 3 and tube 16 of said module 1b and so on until the mechanism of all the modules 11 are locked. However, experience has shown that the system is imperfect with respect to the kinematics, because higher than expected friction occurs between a screw and a nut, the nut being integral with the screw from the outset and the movement firstly relates to the following modules before possibly a complete locking of the latter imposes a resumption of translation of said nut overcoming the friction. Another, possible more serious disadvantage is the presence of stops 8 and 9, which must be equipped with springs to prevent shocks of the nuts 3. The total extension is known, but the stops cause dynamic variations of friction and inertia, which can cause problems in a controlled system. A more regular and foreseeable behaviour of the system is desired.